The aim is to perform structural (morphology, crystal structure, defects,…) and chemical analyses of nanostructures (thin films, 2 dimensional heterostructures, quantum dots (QDs), nanowires) obtained by Molecular Beam Epitaxy (MBE) or Metal Organic Vapor Deposition (MOCVD) to improve the understanding of the growth mechanisms as well as their optical and electro-optical properties.
1) X-ray diffraction
The laboratory develops several X-ray techniques dedicated to the study of nanomaterials at the ESRF (European Synchrotron Research Facility) in particular in the two French CRG beamlines BM32 and BM02. The aim is to reveal the structure of semiconductor heterostructures for example multiple quantum wells, quantum dots and wires. Some materials have been studied in details, very recently GaN/InGaN, GaN/AlGAN, InAs/GaAs and InAs/InP wires with longitudinal or transversal heterostructures. Playing with the versatility of synchrotron radiation in terms of wavelength and beam size and using state of the art setups (goniometers and controlled environments) several topics are presently under study. Most of these works try to resolve the strain and composition field in complex structures and their respective couplings. For this purpose, we use regularly :
Grazing Incidence X-ray Diffraction (GIXRD) mappings to enhance the sensitivity to the surface.
Anomalous measurements (i.e. change of energy) to have a chemical signature in the diffraction that can be unified with absorption effects with the Diffraction Anomalous Fine Structure (DAFS) method.
Coherence Diffraction Imaging (CDI) to analyze strain fields in nanostructures with focused beams.
Grazing Incidence Small Angle X-ray Scattering (GISAXS) to analyze the shape and distributions of the object assembly.
Micro-Laue to map the strain under polychromatic illumination.
Micro or nanobeams in diffraction or fluorescence. Moreover, some of these experiments are performed under specific environments. For example, in situ growths have been performed under the beam in an ultra-high vacuum chamber to study the formation of nitride quantum dots and wires.
Contacts : Joël Eymery
Collaboration : V. Favre-Nicolin (CEA et UGA), F. Rieutord (CEA), H. Renevier (LMGP-INPG).
2) Electron microscopy
Transmission Electron Microscopy (TEM)
Microstructural analyses are performed using the CEA-Plate-Forme de Nano-Caractérisation (PFNC) equipments for sample preparation (polishing, ion milling, Focussed Ion Beam (FIB),…) and TEM investigations (Jeol 4000EX 400kV, Jeol 3010 300kV, Probe corrected-FEI Titan 80-300kV, Probe and Image corrected FEI Titan Pico 80-300kV with monochromator).
The technics used involve conventional TEM imaging, High Resolution TEM (HR-TEM), High Resolution Scanning TEM (HR-STEM) with High Angle Annular Dark Field (HAADF) and Annular Bright Field (ABF) detectors, Energy Filtered Imaging (EFTEM) as well as EDX (Energy Dispersive x-ray) and EELS (Electron Energy Loss) spectroscopy. General information on TEM can be found for example here
Our main studies concern :
Analyses of defects in heterostructures (dislocations, stacking faults,…)
Strain mapping from HR-TEM or HR-STEM images using Geometrical Phase Analysis (GPA) and understanding of the strain relaxation mechanisms (elastic or plastic)
Chemical composition determination at the local scale in case of interfaces, clusters, quantum dots,..
Scanning Electron Microscopy (SEM) with EDX analysis
This is routinely used to characterize the morphology and the chemical composition of the samples after synthesis
Three equipments are available :
Zeiss SEM with Brücker EDX detector and Hitachi D5500 SEM with EDX at the CEA-PFNC. These two instruments allow imaging in STEM mode
Zeiss Ultra + SEM at Institut Néel
People Catherine Bougerol, R. André, H. Boukari, B. Daudin, H. Mariette, S. Tatarenko, T. Aichele, B. Amstatt, S. Founta, L. Maingault, R. Najjar, I.C. Robin Overview and results The goal of our electron microscopy work has been to obtain structural informations at the atomic scale on... > suite